Fiber optic splice housing and integral dry mate connector system

ABSTRACT

A fiber optic splice housing and integral dry mate connector system. In a described embodiment, a fiber optic connection system includes optical fiber sections in respective conduit sections. Each of the conduit sections is received in the housing assembly. An optical connection between the optical fiber sections is positioned within the housing assembly.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. application Ser. No. 12/633,333filed on 8 Dec. 2009, which is a division of prior application Ser. No.10/873,849 filed on Jun. 22, 2004, now issued U.S. Pat. No. 7,641,395.The entire disclosures of these prior applications are incorporatedherein by this reference.

BACKGROUND

The present invention relates generally to operations performed andequipment utilized in conjunction with subterranean wells and, in anembodiment described herein, more particularly provides a fiber opticsplice housing and integral dry mate connector system.

Optical connections between sections of optical fiber can be used inwell completions, such as gravel pack completions. Unfortunately, eachoptical connection will result in some optical transmission loss. Forthis reason, the use of optical connections should be minimized, oravoided, if possible.

While running a completion string into a well, with an optical fiber ina conduit strapped to the completion string, a mishap may cause theconduit and/or the optical fiber to become damaged. If a considerablelength of the conduit has already been run into the well when the damageoccurs, then this may be a situation in which it would be preferable touse an optical connection between sections of the optical fiber, withthe resultant optical transmission loss, rather than go to the expenseof pulling the considerable length of conduit out of the well andreplacing it.

Where an optical distributed temperature sensing system includes anoptical connection between sections of optical fiber, the opticalconnection also results in an effective “blinding” of the system totemperature determinations in a significant length of the optical fiberbelow the optical connection. Therefore, it would be desirable to beable to store the significant length of the optical fiber below theoptical connection in a convenient location downhole, so that theinability of the system to sense temperature in this length of opticalfiber would not impair the system's ability to sense temperature alongan interval in the well.

Typical optical distributed temperature sensing systems use estimationsof a characteristic of an optical fiber known as “differentialattenuation” in calculating temperature along the optical fiber based onoptical signals returned by the optical fiber. It would be desirable tobe able to directly determine a value for the differential attenuationof an optical fiber downhole, or to calibrate a distributed temperaturesensing system by adjusting the value of differential attenuation usedby the system in calculating temperature, in order to accuratelycalibrate the system.

Furthermore, it would be desirable to provide improved opticalconnections and connection systems which will reduce the opticaltransmission loss due to such connections, enhance the convenience inmaking such connections, increase the reliability of such connections,etc.

SUMMARY

In carrying out the principles of the present invention, in accordancewith one of multiple embodiments described below, improved opticalconnections and connection systems are provided. Methods are alsoprovided for calibrating distributed temperature sensing systems, andfor storing substantial lengths of optical fiber downhole.

In one aspect of the invention, a fiber optic connection system isprovided which includes optical fiber sections in respective conduitsections. Each of the conduit sections is received in the housingassembly. An optical connection between the optical fiber sections ispositioned within the housing assembly.

In another aspect of the invention, a method of optically connectingoptical fiber sections to each other is provided. The method includesthe steps of: positioning each of the optical fiber sections within arespective conduit section; optically connecting the optical fibersections to each other using an optical connection; and containing theconnection within a housing assembly.

In yet another aspect of the invention, a fiber optic connectionapparatus is provided which includes optical fiber sections inrespective conduit sections. Each of the conduit sections is received ina respective one of opposite ends of a housing assembly, so that thehousing assembly is reciprocably displaceable over the conduit sections.An optical connection is formed between the optical fiber sections.

A fiber optic connection is provided by the present invention. The fiberoptic connection includes a fiber optic connector having an opticalfiber section therein. A conduit is attached to the fiber opticconnector, with the optical fiber section extending through the conduit.In another aspect of the invention, the fiber optic connector is sealedso that fluid flow through the fiber optic connector is prevented.

An optical fiber storage apparatus is also provided by the presentinvention. The apparatus includes a generally tubular body having atleast one circumferentially extending recess formed thereon. At leastone optical fiber section is received in the recess.

In a further aspect of the invention, a method of calibrating an opticaldistributed temperature sensing system for differential attenuationincludes the steps of: positioning an optical fiber in a wellbore; andstoring a substantial length of the optical fiber in a storage apparatusin the well, so that the substantial length of the optical fiber is at asame temperature in the well.

In a still further aspect of the invention, an optical distributedtemperature sensing system is provided. The system includes an opticalfiber extending along an interval, so that portions of the optical fiberare exposed to different temperatures in the interval. A storageapparatus has a substantial length of the optical fiber stored therein,so that the substantial length of the optical fiber is at a sametemperature in the storage apparatus.

In another aspect of the invention, the optical distributed temperaturesensing system may include a temperature sensing element positioned sothat the temperature sensing element is at the same temperature as thesubstantial length of the first optical fiber. The temperature sensingelement may be internal or external to the storage apparatus,independent of the optical fiber, and may be an optical, electrical ormechanical device. The temperature sensing element may be formed onanother optical fiber of the apparatus.

These and other features, advantages, benefits and objects of thepresent invention will become apparent to one of ordinary skill in theart upon careful consideration of the detailed description ofrepresentative embodiments of the invention hereinbelow and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partially cross-sectional view of an applicationfor a fiber optic connection system embodying principles of the presentinvention;

FIG. 2 is an enlarged scale schematic elevational view of the fiberoptic connection system usable in the application of FIG. 1, theconnection system embodying principles of the present invention;

FIG. 3 is a further enlarged scale schematic partially cross-sectionalview of a fusion splice fiber optic connection apparatus embodyingprinciples of the present invention;

FIG. 4 is a further enlarged scale schematic cross-sectional view of adry mate fiber optic connection embodying principles of the invention;

FIG. 5 is a schematic cross-sectional view of the fiber optic connectionapparatus of FIG. 3, having the dry mate fiber optic connection of FIG.4 therein;

FIG. 6 is a schematic cross-sectional view of another fiber opticconnection apparatus having both the dry mate fiber optic connection ofFIG. 4 and fusion splice connection of FIG. 3 therein;

FIG. 7 is a schematic cross-sectional view of a fiber storage apparatusembodying principles of the invention;

FIG. 8 is an elevational view of a body of the system of FIG. 7;

FIG. 9 is a schematic view of a fiber optic calibration system embodyingprinciples of the invention; and

FIG. 10 is a graph of temperature versus length along fiber for thecalibration system of FIG. 9.

DETAILED DESCRIPTION

Representatively illustrated in FIG. 1 is an application 10 for a fiberoptic connection system 12 depicted in FIG. 2 which embodies principlesof the present invention. In the following description of the system 12and other apparatus and methods described herein, directional terms,such as “above”, “below”, “upper”, “lower”, etc., are used forconvenience in referring to the accompanying drawings. Additionally, itis to be understood that the various embodiments of the presentinvention described herein may be utilized in various orientations, suchas inclined, inverted, horizontal, vertical, etc., and in variousconfigurations, without departing from the principles of the presentinvention. The embodiments are described merely as examples of usefulapplications of the principles of the invention, which are not limitedto any specific details of these embodiments.

As depicted in FIG. 1, a tubular string 14, such as a production tubingstring, is being lowered into a wellbore 16. The tubular string 14 has aconduit 18 externally attached thereto, such as by strapping the conduitto the tubular string as it is lowered into the wellbore 16. It shouldbe understood, however, that the principles of the invention are notlimited to use with a production tubing string or with conduit strappedexternally to a tubing string. The tubular string 14 could instead be acasing, liner, coiled tubing or other type of tubular string, theconduit 18 could be internal to, or in a sidewall of, the tubularstring, use of a tubular string or conduit is not required, etc.

In the application 10, the conduit 18 is a tubular string, such as atype known to those skilled in the art as “control line,” whichtypically has a diameter of approximately ¼ inch. At least one, andpreferably multiple, optical fiber(s) extend through the conduit 18 foruses such as communication, control, sensing, etc.

Due to a mishap during the lowering of the tubular string 14 into thewellbore 16, the conduit 18 has become damaged, such as by severing theconduit into two separate sections 20, 22. Instead of completelysevering the conduit 18, it could be merely crushed or pierced, so thatits pressure-holding or -transmitting capability is questionable. Theoptical fiber(s) within the conduit 18 could also be damaged at the timethe conduit 18 is damaged.

If a considerable length of the tubular string 14 and conduit 18 hasalready been lowered into the wellbore 16 at the time the conduit isdamaged, it may be very expensive to pull the tubular string and conduitout of the wellbore, replace the conduit, and run the tubular string andconduit back into the wellbore. Using the principles of the presentinvention, the decision can be made to instead repair the damagedconduit 18 and/or optical fibers therein by means of the connectionsystem 12 illustrated in FIG. 2.

As representatively illustrated in FIG. 2, the two conduit sections 20,22 have been removed, at least partially, from the tubular string 14.Preferably, ends of the conduit sections 20, 22 are taken to a work areaa safe distance from the rig floor in a non-hazardous environment. Theends of the conduit sections 20, 22 are secured to a work surface 24(such as a shop table), using clamps, vises or other gripping devices26, 28.

If an optical fiber 30 within the conduit 18 has been damaged, it willbe spliced using a fusion splicer 32. To allow access to the opticalfiber 30 by the fusion splicer 32, approximately 12 inches of space maybe needed between the ends of the conduit sections 20, 22. The fusionsplicer 32 is preferably mounted using a device 34, such as atelescoping or otherwise translating base, which enables the fusionsplicer to be smoothly and accurately moved between a position about theoptical fiber 30 and intermediate the ends of the conduit sections 20,22, and a position distanced from the conduit sections as depicted inFIG. 2.

Prior to using the fusion splicer 32 to form a fusion splice connection36 in the optical fiber 30, a housing assembly 38 is slid over the endsof the conduit sections 20, 22. The housing assembly 38 shown in FIG. 2includes a generally tubular housing 40 and two gripping and sealingdevices 42, 44. Many other configurations of housing assemblies may beused in keeping with the principles of the invention.

The housing assembly 38 is used in the connection system 12 to securethe conduit sections 20, 22 to each other, protect the optical fiber 30and fusion splice 36 therein, and to isolate the optical fiber andinterior of the conduit 18 from well pressure and well fluids. Asdepicted in FIG. 2, the housing 40 and one of the devices has beeninstalled over the conduit section 22 and displaced to a position nearthe gripping device 28. The other device 42 has been installed over theconduit section 20 and displaced to a position near the gripping device26. In these positions, the housing assembly 38 is out of the way of useof the fusion splicer 32.

The fusion splicer 32 can now be displaced by the device 34 to aposition in which the optical fiber 30 is received in the fusionsplicer, so that the splice 36 can be formed. Note that it is notnecessary for the fusion splice 36 to be used, since other types offiber optic connections can be used in keeping with the principles ofthe invention. For example, a dry mate type of connection, such as theconnection depicted in FIGS. 4-6 and described below, may be used inplace of the fusion splice 36. However, the fusion splice 36 ispresently preferred, due to its relatively low optical transmissionloss.

After the fusion splice 36 is formed in the optical fiber 30, the fusionsplicer 32 is displaced back out of the way to allow the housingassembly 38 to be displaced over the splice. At this point, it may bedesirable to remove any slack in the optical fiber 30, so that tightradius bends in the optical fiber are avoided. To accomplish this, thegripping device 26 may be displaced away from the other gripping device28 to thereby increase the distance between the ends of the conduitsections 20, 22. For example, a laterally translating base 46 may beused to displace the gripping device 26 away from the other grippingdevice 28.

When the slack in the optical fiber 30 has been removed, the housing 40is displaced to a position in which the splice 36 is within the housing,and the ends of the conduit sections 20, 22 are received in respectiveopposite ends of the housing. An enlarged cross-sectional view showingthis position is depicted in FIG. 3. In this view, multiple opticalfibers 30, 48 are shown extending through the conduit 18, with thesplice 36 operatively connecting sections 50, 52 of the optical fiber30, and another fusion splice 58 operatively connecting sections 54, 56of the optical fiber 48. Thus, it will be appreciated that multipleoptical fibers can be used in a conduit in the connection system 12.

After positioning the housing 40 as shown in FIG. 3, the devices 42, 44are used to grip the ends of the conduit sections 20, 22 and seal offthe interior of the housing. The devices 42, 44 may be conventional tubefittings, for example, of the type sold by Swagelock Company of Solon,Ohio. Alternatively, the devices 42, 44 may be special proprietaryfittings, such as FMJ fittings available from WellDynamics, Inc. ofSpring, Texas, which fittings utilize multiple metal-to-metal seals toensure long term reliability in downhole environments.

Preferably, the housing 40 has an internal dimension ID (such as aninternal diameter) between its opposite ends 60, 62 which is greaterthan an internal dimension id (such as an internal diameter) at one orboth of the ends. In this manner, the interior of the housing 40 canaccommodate deformed ends of the conduit sections 20, 22 (such as mayresult from damage to the conduit 18) without requiring time-consumingstraightening of the ends of the conduit sections received in thehousing. The opposite ends 60, 62 of the housing 40 may be reduced insize to form the internal dimensions id by, for example, swaging theends, cold working, hot forging, or any mechanical deforming process,etc.

The reduced internal dimensions id are preferred for use with theWellDynamics FMJ fittings discussed above. However, it should beunderstood that the reduced internal dimensions id are not necessary inkeeping with the principles of the invention. Furthermore, it is notnecessary for both of the opposite ends 60, 62 to have the reducedinternal dimensions id. For example, only one of the ends 60, 62 couldhave the reduced internal dimension id, while the other end could havean internal dimension equal to, or greater than, the internal dimensionID.

The housing assembly 38, conduit sections 20, 22, optical fiber sections50, 52, 54, 56, and fusion splice connection 108 depicted in FIG. 3comprise a fiber optic connection apparatus 69 which may also be used infiber optic connection systems other than the system 12 in keeping withthe principles of the invention.

Referring additionally now to FIG. 4, another fiber optic connection 70which may be used in the system 12 is representatively illustrated. Theconnection 70 could also be used in other systems and/or in otherapplications, without departing from the principles of the invention.Since some of the elements of the connection 70 are similar to thosedescribed above, the same reference numbers are used to indicate theseelements in FIG. 4.

Instead of using a fusion splice to join sections of optical fiber, theconnection 70 is of the type known to those skilled is the art as a “drymate” connection. Ends of the optical fiber sections 50, 52 and 54, 56are precisely aligned, so that light may be transmitted therebetween.For this purpose, the connection 70 includes two fiber optic connectors72, 74 which, when operatively connected to each other, align therespective optical fiber sections 50, 52 and 54, 56.

The connector 72 has the optical fiber sections 50, 54 extending thereinfrom within the conduit 20 to ferrules 76, 78 positioned in a body 80 ofthe connector. The optical fiber sections 50, 54 may be attached to theferrules 76, 78 by, for example, bonding each optical fiber sectionwithin the respective ferrule.

The ferrule 76 is recessed inwardly from an end 82 of the body 80 of theconnector 72. The ferrule 76 is received in an alignment sleeve 84,which is also recessed in the end 82 of the body 80. However, theferrule 76 is recessed further than the alignment sleeve 84, so that thealignment sleeve can also receive therein another ferrule 86 of theother connector 74 as described below.

The ferrule 78 extends outwardly from the body 80 at a recessed shoulder88 formed on the body. The shoulder 88 is recessed inward relative tothe end 82 of the body 80. In this manner, the ferrule 78 can bereceived in another alignment sleeve 90 recessed in an end 92 of a body94 of the other connector 74.

Another ferrule 96 in the body 94 of the connector 74 is received in thealignment sleeve 90. The ferrule 96 is recessed further into the end 92of the body 94 than the alignment sleeve 90 to allow insertion of theferrule 78 into the alignment sleeve. The optical fiber section 56 isattached to the ferrule 96, for example, by being bonded therein. Whenthe ferrules 78, 96 are both received in the alignment sleeve 90, theyare precisely aligned with each other, so that the optical fibersections 54, 56 are also precisely aligned end-to-end, therebypermitting optical transmission therebetween.

The ferrule 86 extends outwardly from the body 94 at a recessed shoulder98 formed on the body. The shoulder 98 is recessed relative to the end92 of the body 94. The optical fiber section 52 is attached to theferrule 86, for example, by bonding the optical fiber section within theferrule. When the connectors 72, 74 are operatively connected, theferrule 86 is received in the alignment sleeve 84, which preciselyaligns the ferrules 76, 86, thereby precisely aligning the optical fibersections 50, 52 end-to-end and permitting optical transmissiontherebetween.

Preferably, the ferrule 86 does not extend outward from the body 94beyond the end 92, and the ferrule 78 does not extend outward from thebody 80 beyond the end 82, so that the ferrules are protected by theends of the connectors 72, 74 prior to connecting the connectors to eachother. More preferably, the ferrules 78, 86 are recessed relative to therespective ends 82, 92 for enhanced protection of the ferrules.

A biasing device 100, such as a coiled compression spring, may be usedto bias the ferrule 76 into very close proximity, or actual contact,with the ferrule 86 when the connectors 72, 74 are connected. Similarly,another biasing device 102 may be used to bias the ferrule 96 into veryclose proximity, or actual contact, with the ferrule 78.

A seal 104 may be used to prevent fluid flow through the body 80 of theconnector 72. The seal 104 preferably prevents any well fluid orpressure which might enter the connector 72 from passing into theconduit section 20. The seal 104 could be entirely disposed within thebody 80, as depicted in FIG. 4, or it could be partially or entirelydisposed within the end of the conduit section 20.

The seal 104 could be a hardenable fluid which is flowed about theoptical fiber sections 50, 54 in the body 80, and is then allowed toharden. A material such as epoxy could be used for this purpose. Othermaterials, such as elastomers, non-elastomers, etc., could be used inaddition, or as an alternative. A similar seal 106 may be used in thebody 94 of the connector 74 and/or in the end of the conduit section 22to prevent fluid flow through the body 94, and to prevent passage ofwell fluid and pressure into the conduit section.

The body 80 may be attached to the end of the conduit section 20 usingany of a variety of methods. For example, the body 80 could be welded tothe end of the conduit section 20, the body could be threaded into theconduit section, a fastener (such as a pin, dowel, screw, rivet, etc.)could be used to fasten the body to the conduit section, the body couldbe molded onto or into the end of the conduit section, etc.

Any means of attaching or connecting the body 80 to the conduit section20 may be used in keeping with the principles of the invention.Preferably, this attachment prevents fluid from flowing between the body80 and the conduit section 20. The body 94 may be similarly attached tothe end of the conduit section 22.

If the bodies 80, 94 are molded parts, then the seals 104, 106 may beformed integrally with the bodies in the molding process. It is notnecessary for the seals 104, 106 to be elements separate from the bodies80, 94 in keeping with the principles of the invention.

Although the connection 70 is depicted in FIG. 4 as being used toconnect two pairs of optical fiber sections 50, 52, 54, 56, it should beunderstood that any number of optical fiber sections may be connected inkeeping with the principles of the invention. Three pairs of opticalfiber sections may be connected using a connection similar to theconnection 70, without exceeding the outer diameter of a conventionalcontrol line tubing.

Referring additionally now to FIG. 5, the connection is depicted as itmay be used in the system 12. The connection 70 is positioned within thehousing assembly 38. The devices 42, 44 grip and seal to the respectiveconduit sections 20, 22 on either side of the connection 70. In thismanner, the connection 70 is isolated from well fluids and pressures bythe housing assembly 38. If, however, the housing assembly 38 shouldbecome damaged or leak, the seals 104, 106 in the connectors 72, 74 willprevent the well fluids and pressures from entering the conduit sections20, 22.

If the connection 70 is used in the system 12 in place of the fusionsplice connection 108 (fusion splices 36, 58) described above, then ofcourse the fusion splicer 32 would not be used. The housing 40 may alsobe made somewhat shorter, since there is no need to accommodate thefusion splicer 32 between the ends of the conduit sections 20, 22. It isbelieved that the fusion splice connection 108 would be most suitablyused for repairs or otherwise unanticipated connections, whereas the drymate connection 70 would be most suitably used for pre-plannedconnections, but either connection could be used in either situation inkeeping with the principles of the invention.

The housing assembly 38, conduit sections 20, 22, and dry mateconnection 70 depicted in FIG. 5 comprise a fiber optic connectionapparatus 109 which may also be used in fiber optic connection systemsother than the system 12 in keeping with the principles of theinvention.

Referring additionally now to FIG. 6, another connection system 110 isrepresentatively illustrated. The system 110 is similar in some respectsto the system 12 described above, and so elements which are similar tothose described above are indicated in FIG. 6 using the same referencenumbers.

The system 110 includes both a fusion splice connection 108 and a drymate connection 70 positioned within a housing assembly 112. Unlike thehousing assembly 38 described above, the housing assembly 112 includesmultiple generally tubular housings 114, 116. The fusion spliceconnection 108 is positioned within the housing 114, and the dry mateconnection 70 is positioned within the housing 116.

The housings 114, 116 are connected to each other at a pressure-tightconnection 118, which may include one or more metal-to-metal seals. Theconnection 118 could, for example, be configured similar to aWellDynamics FMJ fitting.

The connection system 110 permits the connector 72 of the dry mateconnection 70 to be connected to optical fibers in the conduit section20 in the field. This may be advantageous where a well tool, such as apacker, valve, etc., is supplied to the field with the dry mateconnector already installed, and optical fibers in the conduit section20 are to be connected to optical fibers in the well tool. In thatsituation, the housing 116 depicted in FIG. 6 may be considered as thewell tool having the connector 74 pre-installed therein. The housing 116could alternatively be attached to the conduit 22 external or internalto a well tool.

To make the optical connection, the housing 116 would be secured, suchas by using the device 28 shown in FIG. 2. The connector 72 would beconnected to the connector 74. The conduit section 20 would be secured,such as by gripping it with the device 26. The housing 114 and device 42would be slid over the conduit section 20. The fusion splicer 32 wouldthen be used to form the splices 36, 58 between the optical fibers inthe conduit section 20 and the optical fibers in the connector 72. Thetranslating base 46 would be used to displace the device 26 away fromthe device 28 to remove slack from the optical fibers. The housing 114would be attached and sealed to the housing 116 at the connection 118.The device 42 would be used to attach and seal the housing 114 to theconduit section 20.

This is similar to the method described above for forming the fusionsplice connection 108 in the system 12. A main difference in the system110 is that the housing 116 and dry mate connection 70 are interposed toone side of the fusion splice connection 108. Note that in the system110 it is not necessary for the conduit section 22 to be used, since theoptical fibers therein could instead terminate in the housing 116, orcould be otherwise positioned.

The housing assembly 112, conduit sections 20, 22, dry mate connection70, and fusion splice connection 108 depicted in FIG. 6 comprise a fiberoptic connection apparatus 119 which may also be used in fiber opticconnection systems other than the system 110 in keeping with theprinciples of the invention.

Referring additionally now to FIG. 7, a fiber storage apparatus 120 isrepresentatively illustrated. In situations where a connection is madebetween optical fibers used downhole, it may be desirable to store asubstantial length of optical fiber. For example, in a distributedtemperature sensing system, the temperature of approximately 1 meter ofoptical fiber might not be effectively sensed beyond a fusion spliceconnection, and the temperature of at least approximately 10 meters ofoptical fiber might not be effectively sensed beyond a dry mateconnection.

Thus, it would be beneficial to be able to store at least one meter, andpreferably 10-50 meters or more, of optical fiber beyond an opticalconnection in a distributed temperature sensing system. In such asystem, it would be desirable to store the substantial length of opticalfiber after the optical connection in the fiber without causing anysharp radius bends in the fiber, which might lead to premature failureof the fiber. Note that the fiber storage apparatus 120 could be used inapplications other than distributed temperature sensing systems, inkeeping with the principles of the invention.

The fiber storage apparatus 120 includes a generally tubular body 122and a generally tubular outer housing 124. The body 122 and housing 124are configured for interconnection in a tubular string, such as thetubular string 14 described above, so that a flow passage 126 of thetubular string extends through the body and housing. Any type of tubularstring could be used with the apparatus 120 (such as production tubing,casing, liner or coiled tubing strings, etc.), but it is not necessaryfor the body 122 and housing 124 to be interconnected in a tubularstring in keeping with the principles of the invention.

The body 122 has gripping and sealing devices 128, 130 installed at anupper end thereof for attaching conduit sections 132, 134 to the body.The devices 128, 130 could be similar to, or the same as, the devices42, 44 described above. The conduit sections 132, 134 could be similarto, or the same as, the conduit sections 20, 22 described above.

An optical fiber section 136 extends through the conduit section 132 andinto the body 122 via a passage 140. Another optical fiber section 138extends through the conduit section 134 and into the body 122 viaanother passage 142. The optical fiber sections 136, 138 may be separatesections of an optical fiber which are connected via a fusion spliceconnection (such as the fusion splices 36, 58 described above) or a drymate connection (such as the connection 70 described above), or theoptical fiber sections could be connected in another manner.Alternatively, the optical fiber sections 136, 138 could be the same,i.e., a continuous length of optical fiber, instead of being separatesections of an optical fiber.

If the optical fiber sections 136, 138 are separate connected sectionsof an optical fiber, then the connection between the optical fibersections may be contained within the storage apparatus 120, as describedbelow. However, it should be understood that it is not necessary for anyconnection between the optical fiber sections 136, 138, if any, to becontained within the storage apparatus 120 in keeping with theprinciples of the invention.

Each of the passages 140, 142 intersects an annular circumferentiallyextending recess 144 formed externally on the body 122. Anothersimilarly configured recess 146 is formed on the body 122 spaced apartfrom the recess 144. Prior to installing the housing 124 on the body 122as depicted in FIG. 7, the optical fiber sections 136, 138 are woundabout the body in the recesses 144, 146 to thereby store a substantiallength of optical fiber in the recesses. The housing 124 is theninstalled over the recesses 144, 146 and sealed to the body 122 aboveand below the recesses, preferably using one or more metal-to-metalseals and/or elastomeric or non-elastomeric seals 148, 150. Preferably,the optical fiber sections 136, 138 and the interior of the apparatus120 are thus maintained at atmospheric pressure when the apparatus isinstalled in a well.

Referring additionally to FIG. 8, a manner in which the optical fibersections 136, 138 may be wound about the body 122 is representativelyillustrated. In FIG. 8, the body 122 and optical fiber sections 136, 138are shown apart from the remainder of the apparatus 120 for illustrativeclarity. The body 122 is also rotated somewhat about its vertical axis,so that the manner in which the optical fiber section 136 extendsthrough the passage 140 and recesses 144, 146 can be clearly viewed.

Note that the optical fiber section 136 extends downwardly through thepassage 140 to the recess 144. The optical fiber section 136 thenextends in another curved recess 152 which interconnects the recesses144, 146. The optical fiber section 136 extends only briefly in therecess 146 before extending in another curved recess 154 which alsointerconnects the recesses 144, 146. The recess 154 permits the opticalfiber section 136 to extend back up to the recess 144.

In this manner, the optical fiber section 136 is directed through thepassage 140 and recesses 152, 146, 154 to the recess 144. The opticalfiber section 136 is thus received in the upper recess 144 withoutmaking any sharp radius bends which might break, otherwise damage orcause long term reliability problems. The other optical fiber section138 is similarly directed through the passage 142 and another curvedrecess (similar to the recess 152) to the lower recess 146 withoutmaking any sharp radius bends.

With the optical fiber section 136 received in the upper recess 144 andthe optical fiber section 138 received in the lower recess 146, theoptical fiber sections can now be simultaneously wound multiple timesabout the body, thereby storing multiple wraps of the optical fibersection 136 in the upper recess 144, and multiple wraps of the opticalfiber section 138 in the lower recess 146. Thus, this configuration ofthe body 122 permits a substantial length of the optical fiber sections136, 138 to be stored in the apparatus 120.

An equal or greater length of either of the optical fiber sections 136,138 relative to the other of the optical fiber sections could be storedin the apparatus 120 in keeping with the principles of the invention. Asdepicted in FIG. 8, a greater length of the optical fiber section 136 iswrapped about the body 122 as compared to the length of the opticalfiber section 138.

An optical connection 156, such as a fusion splice, between the opticalfiber sections 136, 138 is received in the lower recess 146. At thecompletion of the process of wrapping the optical fiber sections 136,138 about the body 122, the optical fiber section 136 is received inanother curved recess 158 interconnecting the upper and lower recesses144, 146. If the lengths of the optical fiber sections 136, 138 wrappedabout the body 122 were approximately equal, then the connection 156could be received in the recess 158.

Although the apparatus 120 has been illustrated as including the body122 on which the optical fiber sections 136 are externally wrapped, andthe housing 124 which outwardly contains and protects the optical fibersections received in the external recesses 144, 146, 152, 154, 158formed on the body, it should be clearly understood that many otherconfigurations are possible in keeping with the principles of theinvention. For example, the optical fiber sections 136, 138 could bereceived internally on the body 122 (in which case the housing 124 couldinwardly contain and protect the optical fiber sections), or the opticalfiber sections could be received in a sidewall of the body (in whichcase a separate protective housing may not be used), etc. It is also notnecessary for the devices 128, 130 and passages 140, 142 to bepositioned at one end of the body 122. One of the devices 128, 130 andthe respective one of the passages 140, 142 could instead be positionedat an opposite end of the body 122.

Furthermore, additional optical fibers and/or optical fiber sectionscould be received or stored in a single storage apparatus 120. Forexample, if the optical fiber sections 136, 138 are part of adistributed temperature sensing system, then they may be of the typeknown to those skilled in the art as multi-mode optical fibers. It maybe beneficial to also position an optical fiber of the type known tothose skilled in the art as a single mode optical fiber in the apparatus120 to provide an independent temperature sensing capability, to provideinformation for calibrating the distributed temperature sensing system,or for other purposes. Thus, multiple single mode and/or multi-modeoptical fibers, and any combination of these, may be received in thestorage apparatus 120 in keeping with the principles of the invention.

Referring additionally now to FIG. 9, a schematic depiction of a methodof calibrating an optical distributed temperature sensing system 160 isrepresentatively illustrated. The temperature sensing system 160includes multiple storage apparatuses 120. Each of the storageapparatuses 120 has a substantial length 166 of a multi-mode opticalfiber 162 stored therein. Also received in each storage apparatus 120 isa single mode optical fiber 164.

The optical fiber 162 may comprise multiple optical fiber sections 184,and the optical fiber 164 may comprise multiple optical fiber sections186. Alternatively, the optical fibers 162, 164 could each be a singlelength of optical fiber, without being divided into sections.

The substantial lengths 166 of the optical fiber 162 are each locatedbelow a respective one of multiple optical connections 168interconnecting the sections 184. As discussed above, an opticaldistributed temperature sensing system is effectively “blinded” for asubstantial length beyond an optical connection. Thus, by compactlystoring the substantial lengths 166 of the optical fiber 162 below eachconnection 168 in the storage apparatuses 120, this blinding of thesystem 160 below each connection does not significantly compromise theability of the system to detect temperature along an interval below theconnection.

However, it should be understood that the apparatuses 120 can be usedwhether or not the connections 168 are formed in the optical fiber 162.There are other reasons why it may be beneficial to store thesubstantial lengths 166 of the optical fiber 162 in the system 160, orin systems other than optical distributed temperature sensing systems.For example, the compact storage of a substantial length of the opticalfiber 162 can provide valuable information for calibrating an opticaldistributed temperature sensing system.

In the system 160, a parameter known to those skilled in the art as adifferential attenuation value used in calculating temperature along theoptical fiber 162 may be accurately adjusted using the substantiallengths 166 of the optical fiber stored in the storage apparatuses 120,so that the system is more precisely calibrated. Referring additionallynow to FIG. 10, an idealized graph of temperature (T) versus length (L)along the optical fiber 162 for the system 160 of FIG. 9 isrepresentatively illustrated.

In this idealized graph 170, for clarity it is assumed that theconnections 168 are not present in the optical fiber 162, and the upperstorage apparatus 120 is located at the surface at the beginning of theoptical fiber. Surface temperature is at T=0. A horizontal line 172extends from the origin (L=0, T=0) on the graph 170, indicating that thetemperature of the entire substantial length 166 of the optical fiber162 in the storage apparatus 120 at the surface is the same.

A positively sloped line 174 indicates that the temperature of theoptical fiber 162 increases gradually between the storage apparatus 120at the surface and the next deeper storage apparatus. Another horizontalline 176 indicates that the temperature of the entire substantial length166 of the optical fiber 162 in the storage apparatus 120 below thesurface storage apparatus is at a same temperature.

Another positively sloped line 178 on the graph 170 again indicates thatthe temperature of the optical fiber 162 increases gradually between thetwo storage apparatuses 120 below the surface storage apparatus. Yetanother horizontal line 180 indicates that the entire substantial lengthof the optical fiber 162 in the deepest storage apparatus 120 is at asame temperature.

If one of the horizontal lines 172, 176, 180 is not horizontal in actualpractice, then this is an indication that the differential attenuationvalue used to calculate temperature along the length of the opticalfiber 162 in the system 160 is in error and should be adjusted. When thedifferential attenuation value used in the system 160 is properlyadjusted, the lines 172, 176, 180 should be horizontal, since the entiresubstantial lengths 166 of the optical fiber 162 in the storageapparatuses 120 should be at respective same temperatures in the well.

In the past, the differential attenuation value used in an opticaldifferential temperature sensing system was based on experience,empirical testing of an optical fiber, etc. In contrast, the system 160allows the differential attenuation value to be directly evaluated foraccuracy in each particular installation. Furthermore, since thedifferential attenuation value can be evaluated for accuracy at multiplelocations in a well (i.e., by using multiple storage apparatuses 120),adjustments in the differential attenuation value may be made fordifferent portions of the optical fiber 162. For example, in the system160, a first differential attenuation value may be used for the opticalfiber 162 near the storage apparatus 120 at the surface, a seconddifferential attenuation value may be used for the optical fiber toeither side of the next deeper storage apparatus, and a thirddifferential attenuation value may be used for the optical fiber toeither side of the deepest storage apparatus. By using separatelyadjusted differential attenuation values in the system 160 forrespective separate lengths of the optical fiber 162, each of the lines172, 176, 180 on the graph 170 can be independently made horizontal.

The single mode optical fiber 164 can have independent temperaturesensing elements 182 located in each of the storage apparatuses 120. Oneor more temperature sensing elements 182 could be located in eachstorage apparatus 120. By positioning the elements 182 in theapparatuses 120, they will preferably be at the same temperature as therespective substantial lengths 166 of the optical fiber 162. Theelements 182 are schematically illustrated in FIG. 9 as being fiberBragg gratings, but any other type of temperature sensing elements maybe used, such as interferometric temperature sensors, etc.

The independent temperature indications provided by the elements 182 canbe used to calibrate the system 160 so that the horizontal lines 172,176, 180 occur at the respective appropriate temperatures on the graph170 (i.e., at the temperatures indicated by the respective elements182). The differential attenuation value adjustments described aboveshould also position each of the lines 172, 176, 180 so that they eachindicate the same temperature as indicated by the respective temperaturesensing elements 182.

If the connections 168 are used in the optical fiber 162, then the graph170 will also show that the system 160 is effectively blinded for asubstantial length beyond each connection. For this reason, each storageapparatus 120 may have stored therein substantially more than the lengthof the optical fiber 162 for which the system 160 is blinded, so thatthe enhanced calibration benefits described above may also be realized.

Although the elements 182 have been described above as being positionedin the storage apparatuses 120, and as being formed on the optical fiber164, other configurations and other types of temperature sensingelements may be used without departing from the principles of theinvention. For example, the elements 182 could be positioned internal orexternal to the apparatuses 120. The elements 182 could be optical,electrical, mechanical or other types of temperature sensing devices.Preferably, however, the elements 182 provide an indication oftemperature which is independent of the distributed temperature sensingwhich is performed using the optical fiber 162.

Of course, a person skilled in the art would, upon a carefulconsideration of the above description of representative embodiments ofthe invention, readily appreciate that many modifications, additions,substitutions, deletions, and other changes may be made to thesespecific embodiments, and such changes are contemplated by theprinciples of the present invention. Accordingly, the foregoing detaileddescription is to be clearly understood as being given by way ofillustration and example only, the spirit and scope of the presentinvention being limited solely by the appended claims and theirequivalents.

What is claimed is:
 1. A method of calibrating an optical distributedtemperature sensing system for differential attenuation, the methodcomprising the steps of: positioning a first optical fiber in awellbore; and storing a substantial length of the first optical fiber ina storage apparatus in the well, so that the substantial length of thefirst optical fiber is at a same temperature in the storage apparatus.2. The method of claim 1, further comprising the step of calibrating thedistributed temperature sensing system, so that a temperature of theentire substantial length of the first optical fiber indicated by thedistributed temperature sensing system is the same.
 3. The method ofclaim 2, wherein the calibrating step further comprises adjusting adifferential attenuation value of the distributed temperature sensingsystem, so that the temperature of the entire substantial length of thefirst optical fiber indicated by the distributed temperature sensingsystem is the same.
 4. The method of claim 1, wherein the storing stepfurther comprises storing multiple substantial lengths of the firstoptical fiber in respective multiple spaced apart storage apparatuses inthe well.
 5. The method of claim 4, further comprising the step ofcalibrating the distributed temperature sensing system, so that atemperature of each entire substantial length of the first optical fiberindicated by the distributed temperature system is the same.
 6. Themethod of claim 5, wherein the calibrating step further comprisesadjusting multiple differential attenuation values of the distributedtemperature system, so that the temperature of each entire substantiallength of the first optical fiber indicated by the distributedtemperature system is the same.
 7. The method of claim 4, furthercomprising the step of disposing multiple temperature sensing elementsin the respective storage apparatuses.
 8. The method of claim 7, furthercomprising the step of calibrating the distributed temperature sensingsystem, so that a temperature of each substantial length of the firstoptical fiber indicated by the distributed temperature sensing system isthe same as a temperature indicated by the respective one of thetemperature sensing elements.
 9. The method of claim 8, wherein thecalibrating step further comprises adjusting multiple differentialattenuation values of the distributed temperature sensing system, sothat the temperature of each entire substantial length of the firstoptical fiber indicated by the distributed temperature sensing system isthe same as the temperature indicated by the respective one of thetemperature sensing elements.
 10. The method of claim 1, furthercomprising the step of disposing a temperature sensing element in thestorage apparatus, so that the temperature sensing element is at thesame temperature in the well as the substantial length of the firstoptical fiber.
 11. The method of claim 10, wherein the disposing stepfurther comprises associating the temperature sensing element with asecond optical fiber in the storage apparatus.
 12. The method of claim11, further comprising the step of forming the temperature sensingelement as a fiber Bragg grating on the second optical fiber.
 13. Themethod of claim 11, wherein in the disposing step, the temperaturesensing element is an interferometric temperature sensor.
 14. The methodof claim 10, further comprising the step of calibrating the distributedtemperature sensing system, so that a temperature of the substantiallength of the first optical fiber indicated by the distributedtemperature sensing system is the same as a temperature indicated by thetemperature sensing element.
 15. The method of claim 14, wherein thecalibrating step further comprises adjusting a differential attenuationvalue of the distributed temperature sensing system, so that thetemperature of the entire substantial length of the first optical fiberindicated by the distributed temperature sensing system is the same asthe temperature indicated by the temperature sensing element.
 16. Themethod of claim 1, wherein in the positioning step, the first opticalfiber comprises a multi-mode optical fiber.